Commercial or office-type chairs, including secretarial and executive chairs, typically employ a chair back of the upholstered type. That is, the chair back employs an inner support panel or shell on which is positioned a suitable cushion, and a covering such as of fabric or vinyl is typically wrapped around the cushion. The outer edge portions of the cushion and covering wrap around the outer edges of the intermediate shell, which outer edge portions of the cushion and covering are normally suitably clamped between the inner shell and the back panel (that is, the outer shell) of the chair back. This outer shell, which defines the exposed exterior rear surface of the chair back, is fixedly anchored to the inner shell by various types of connecting or anchoring structures. While chair backs of this general type have been developed and utilized for many years, nevertheless the fixed connection of the outer shell to the inner shell, and specifically the type of connecting or anchoring structure utilized, has long presented a problem to chair designers. Many of the utilized structures have been less than desirable but have nevertheless been extensively used in view of the difficulties in overcoming the disadvantages.
For example, for many years a great number of chair manufacturers did, and many manufacturers still do, utilize threaded fasteners such as screws for fixedly securing or joining together the inner and outer shells of the chair back. With this type of structure, the outer shell is provided with suitable openings through which the screws extend so that the screws can be threaded to the inner shell, with the screw heads typically being of a configuration so as to seat more or less flush with the outer surface of the outer shell in an attempt to disguise or hide their appearance. Nevertheless, with this arrangement, the screw heads are still visible and hence detract and oftentimes destroy the esthetics of the chair. Further, the installation and securement of the screws between the inner and outer shells is a difficult and time-consuming installation or assembly operation. In addition, if the screws are not properly installed and tightened, they can be accidentally over-tightened and hence cause undesired compression or deflection of the outer shell, particularly since the outer shell is normally molded or formed from plastic or metal, and this thus destroys the appearance of the chair.
In an attempt to avoid use of exposed screws or fasteners, one chair manufacturer has adopted a connecting structure wherein separate connecting parts are glued or adhesively bonded to the opposed surfaces of the inner and outer shells, which parts are then fixedly snapped together during assembly of the chair back so as to fixedly relate the inner and outer shells to one another. With this connecting structure, however, the inner and outer shells are always fixedly related in the same special relationship, inasmuch as this connecting structure provides no adjustability with respect to the spacing between the inner and outer shells. With chair backs, however, this lack of adjustment creates a significant problem inasmuch as the edge of the cushion and/or covering which overlaps and is clamped between the opposed edges of the inner and outer shells may vary substantially from chair to chair. Hence, the desired spacing between the inner and outer shells also suitably varies, depending upon the quantity of cushion and covering clamped between the opposed edges of the shells, in order to achieve optimum clamping of the cushion and covering. The lack of adjustment in this known structure thus can create difficulty in not only assembling some of the chair backs, but can also result in improper securement or clamping of the edges of the cushion and covering.
Another problem encountered with connecting structures of this latter type occurs due to the fact that the outer shell is typically injection molded from a plastic material, specifically polypropylene. Due to the snap-type fixed structural connection between the inner and outer shells, coupled with the variable clamping pressure which it thus creates on the edges of the cushion and covering, the connecting parts which are fixedly secured to the outer shell can cause excessive stress to be imposed on the outer shell, which outer shell may become deformed and thus exhibit stress cracks, commonly referred to as "white-out" on the exterior surface of the outer shell. This thus destroys the appearance, and hence saleability, of the chair.
In a further attempt to avoid use of threaded fasteners and the like so as to provide a blind or hidden connecting structure for joining the inner and outer shells, and at the same time retain at least limited adjustability with respect to the spacing between the inner and outer shells to avoid the problems encountered with the above-mentioned snap-type connecting structure, another chair manufacturer has adopted a hidden or blind type connecting structure which employs what is often referred to as a "Christmas tree" fastener. With this arrangement, the outer shell is provided with several hollow bosses integrally molded on the inner side thereof. The so-called Christmas tree fastener is conventionally molded of plastic and includes a head portion having a large number of circumferentially and axially spaced radial projections. The other end of the fastener is provided with an enlarged base. The enlarged base of the fastener is inserted into the hollow boss, and a conventional washerlike spring clip is passed over the head portion and moved into the enlarged boss. The spring clip has external resilient teeth for gripping the enlarged boss to thereby fixedly lock the base of the Christmas tree fastener to the outer shell. The outer shell, having the Christmas tree fasteners fixed thereto, is then fixedly secured to the inner shell or panel by means of the Christmas tree (i.e., the head portion) being inserted into openings formed in the inner shell. While this arrangement does permit the inner and outer shells to be fixedly secured while at the same time axially adjustably related to compensate for variations in the cushion and/or covering thickness, nevertheless this arrangement is structurally complex since it requires two separate parts for joining the two shells, namely the Christmas tree fastener and the spring clip. This arrangement is also more expensive to manufacture and assemble in view of the complexities involved in molding the Christmas tree fastener, and the additional complications and time required to initially assemble the Christmas tree fastener and spring clip to the outer shell.
Thus, the present invention relates to an improved fastener and connecting structure for joining the inner and outer shells of a chair back while permitting the spacing therebetween to be suitably adjusted, which improved connecting structure overcomes the aforesaid disadvantages.
The improved connecting structure of this invention involves a single fastener for fixedly connecting the inner and outer shells. The connecting structure involves a pinlike projection fixed on and projecting from one of the shells, and a hollow hub fixed on and projecting from the other shell, which hub is adapted to receive the pinlike projection therein. The hub and pinlike projection are axially fixedly connected by the fastener which is formed as a washerlike spring clip having a set of exterior resilient teeth which slope toward one side of the fastener, and a set of interior resilient teeth which slope toward the other side of the fastener. The fastener is initially seated against a shoulder formed within the hub so that the external teeth grippingly engage the hub and prevent removal of the fastener. The pinlike projection can then be axially slidably inserted through the fastener to the desired extent, whereupon the interior teeth grippingly engage the pinlike projection and prevent withdrawal of same. The inner and outer shells are thus fixedly joined together in a manner whereby the outer shell can be a continuous and non-interrupted structure free of visible screws or protrusions, whereupon this improved connecting structure is thus totally hidden and hence effectively constitutes a blind connection. The fastener permits the two shells to be moved toward one another to the extent necessary so as to provide optimum clamping between the edges of the shells for holding the confined edges of the cushion and/or cover. The pinlike projection can thus be inserted into the hub to the extent necessary to achieve optimum clamping of the cushion and/or cover, and the fastener will then fixedly axially secure the pinlike projection and hub together so as to maintain the desired clamping relationship between the opposed edges of the shells.
This improved fastening structure, as it relates to a chair back, is highly desirable since it greatly simplifies the structure of the chair inasmuch as only a single element, namely the washerlike fastener, is necessary for creating the fixed connection between the inner and outer shells, whereupon the number of components and hence both the manufacture and assembly of the chair is substantially minimized. At the same time, this arrangement permits optimum clamping of the cushion and covering between the opposed edges of the shells, and also readily accommodates any variation in the cushion and/or covering, or any variation in the shells, so that the same arrangement can be successfully utilized for large numbers of chairs of either the same or different design or style. The resulting chair is highly advantageous since the exposed exterior surface of the outer shell can be smooth and thus of pleasing appearance, inasmuch as it is free of exposed screw heads and the like, and is also free of any interior connections which may cause undesirable stress cracks inasmuch as the clamping pressure imposed on the cushion edges as trapped between the opposed shell edges can be more precisely controlled and maintained.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.